Forecasting Leaves

My prediction? Well, I’m thinking the leaves are going to be turning early this fall, and I think the colors will be brighter and more spectacular than usual. Here’s why…Let’s first talk about how and why the leaves turn. Leaves don’t actually turn color, they lose it, green to be exact. As the nights become longer, chlorophyll production in the leaf is slowed down, and eventually the chlorophyll is destroyed. Chlorophyll is the green pigment responsible for photosyntesis, the production of sugar in the leaf. As the green disappears, other pigments already in the leaf, previously hidden by the chlorophyll, appear, and the leaves show their “true” color. (I’m simplifying here, one pigment exists, one is made my the sugar built up, but you get the idea.)
Weather does affect leaf color, but only in intensity, and a little bit in timing. Cool but not freezing nights, and warm sunny days speed the destruction of chlorphyll, making the colors more intense. A good growing year with adequate moisture assures healthy leaves going into the fall, while a dry summer may cause the leaves to hang and turn later, while the tree gets as much use out of it’s chlorophyll expenditure as it can. Much rain in the fall can wash the leaves out, muddying the colors, even blowing them right off the trees.
Finally, leaves fall when hormones in the tree cause the petiole to form an ‘abscission zone’ between itself (the leaf stem) and the branch itself. This zone enables the leaf to drop, and seals the channel between leaf and stem, so pathogens can’t enter.
Enough biology, on to the voodoo of my prediction. Let’s look at the growing year this summer. Plenty wet, but not quite too wet like last year (unless you are a corn grower). So, we’ve got good healthy trees going into the fall. And fall so far? Warm days, cool crisp nights. We’re setting ourselves up for great bright fall colors. I’m thinking the timing will be a little early this year. Middlebury at least has been quite dry. The last measurable rain was August 29th. The trees are a little stressed right now, and weaker trees are already turning. In an effort to conserve it’s remaining water, the trees will begin shutting down early, shedding it’s leaves. And I don’t see a pattern shift in the weather for a while, so no reason not to think the drought will continue.